An organic light-emitting diode device, also called an OLED device, commonly includes a substrate, an anode, a hole-transporting layer made of an organic compound, an organic luminescent layer with suitable dopants, an organic electron-transporting layer, and a cathode. OLED devices are attractive because of their low driving voltage, high luminance, wide-angle viewing, and capability for full-color flat emission displays. Tang et al. described this multilayer OLED device in their U.S. Pat. Nos. 4,769,292 and 4,885,211.
A common problem with OLED displays is sensitivity to moisture. They can be particular highly moisture-sensitive electronic devices, and require humidity control to levels below about 1000 ppm and some require humidity control below even 100 ppm.
Numerous publications describe methods or materials for controlling humidity levels within enclosed or encapsulated electronic devices. Kawami et al., in U.S. Pat. No. 5,882,761, has taught the use of a desiccant layer over the organic layers of an OLED display, between the substrate and the top seal. Kawami et al. teach the use of the following desiccants: alkali metal oxides, alkali earth metal oxides, sulfates, metal halides, and perchlorates. Such materials can be deposited in a predetermined shape by such techniques as vacuum vapor deposition, sputtering, or spin-coating. In U.S. Pat. No. 6,226,890, Boroson et al., disclose the use of a castable blend of the above desiccants with a suitable binder. Kawami et al., in the '761 patent, have taught that the drying agent is to be coated on the inside surface of an airtight container. Boroson et al., in the '890 patent, use the castable blend to coat the interior surface of an enclosure. Techniques such as these require additional materials and efforts. In U.S. Patent Application Publication 2003/0110981, Tsuruoka et al., have disclosed a series of transparent drying agents, which operate by chemisorption and can be used in an OLED display. These are conceived as useful in OLED devices wherein one wishes to allow light emission through a desiccant layer. In U.S. Pat. No. 4,081,397, Booe, describes a composition used for stabilizing the electrical and electronic properties of electrical and electronic devices. The composition comprises alkaline earth oxides such as barium oxide in an elastomeric matrix.
To address the moisture-sensitivity problem, an encapsulation container often encloses the OLED device and is secured to the substrate to form an enclosure. Desiccant material is formed on the inside of the enclosure to protect the OLED from moisture. A problem with this arrangement is that when the OLEDs become large in size, the substrate typically has to flex and there is some likelihood that the encapsulation container will come in contact with the OLED. This can cause mechanical damage to one of the electrodes or shorting.